fe: acl0 lab vhost, cluster upstream, INSTALL smoke checklist

Add ac-fe.conf and ac-fe.fragment for Gentoo FE proxy to cast cluster;
upstream uses cast01 primary with cast02/03 backup; document PO install steps.

Co-authored-by: Cursor <cursoragent@cursor.com>

README.md

@@ -1,5 +1,12 @@
 # ac-platform-edge
 
-Nginx route fragments for apps.f0xx.org.
+Nginx route fragments for `apps.f0xx.org` and lab FE (`acl0.f0xx.org`).
+
+| Path | Purpose |
+|------|---------|
+| `fe/ac-fe.conf` | Gentoo FE install → `/etc/nginx/ac-fe.conf` (lab vhost + upstream) |
+| `fe/ac-fe.fragment` | `/issues/` + legacy `/crashes/` redirect; include in prod `apps.conf` when ready |
+| `fe/INSTALL.md` | PO steps (copy, certbot, `nginx.conf` include, reload) |
+| `fragments/crash_reporter/` | BE-side / legacy snippets |
 
 Remote: `git://f0xx.org/ac/ac-platform-edge`